i965: fix PIPE_CONTROL command for gen6.

Signed-off-by: Zou Nan hai <nanhai.zou@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/mesa/drivers/dri/intel/intel_batchbuffer.c

@@ -275,7 +275,16 @@ intel_batchbuffer_emit_mi_flush(struct intel_batchbuffer *batch)
 {
    struct intel_context *intel = batch->intel;
 
-   if (intel->gen >= 4) {
+   if (intel->gen >= 6) {
+      BEGIN_BATCH(4);
+      OUT_BATCH(_3DSTATE_PIPE_CONTROL);
+      OUT_BATCH(PIPE_CONTROL_INSTRUCTION_FLUSH |
+		PIPE_CONTROL_WRITE_FLUSH |
+		PIPE_CONTROL_NO_WRITE);
+      OUT_BATCH(0); /* write address */
+      OUT_BATCH(0); /* write data */
+      ADVANCE_BATCH();
+   } else if (intel->gen >= 4) {
       BEGIN_BATCH(4);
       OUT_BATCH(_3DSTATE_PIPE_CONTROL |
 		PIPE_CONTROL_WRITE_FLUSH |